Penis

The penis of an Asian elephant

A penis (from Latin: penis; plural penises or penes /-niːz/) is the main sexual organ of most male animals. It is used to inseminate females (or hermaphrodites) during sex (copulation).^[1] In some animals, the penis is also used to urinate.

Penises are found in many animal species, mainly warm-blooded mammals. They are found in both vertebrates and invertebrates. Penises are not found in every species of animal. In those species where the male does have a penis, the penises are not homologous. This means that it evolved separately in each species. They also fill with blood so it can fit in the women’s vagina, in a process called ‘erecting’. During sleep, the human penis may have more blood in it than usual, the term for this is called “morning wood”. Once erect, the penis can eject semen through ejaculation.

References

↑ Janet Leonard; Alex Cordoba-Aguilar R (18 June 2010). The Evolution of Primary Sexual Characters in Animals. Oxford University Press. ISBN 978-0-19-971703-3. Retrieved 20 July 2013.

[SciencesMexico2010-1] Janet Leonard; Alex Cordoba-Aguilar R (18 June 2010). The Evolution of Primary Sexual Characters in Animals. Oxford University Press. ISBN 978-0-19-971703-3. Retrieved 20 July 2013.

[1]

Human reproductive system
Female anatomy	Female reproductive system – Breasts – Cervix – Clitoris – Fallopian tubes – Bartholin's glands – Gräfenberg spot (G-spot) – Hymen – Labia – Ovaries – Skene's glands – Urethra – Uterus – Vagina – Vulva
Female physiology	Menstruation – Pregnancy – Childbirth – Lactation – Estrogen – Orgasm – Ovum
Male anatomy	Male reproductive system – Bulbourethral glands – Corpus cavernosum – Ejaculatory ducts – Epididymis – Foreskin – Frenulum – Glans penis – Penis – Prostate – Rete testis – Scrotum – Seminal vesicles – Seminiferous tubules – Sertoli cell – Spermatic cord – Testicles (testes) – Urethra – Vasa deferens (Vas deferentia)
Male physiology	Ejaculation – Erection – Orgasm – Semen – Sperm – Testosterone
Anatomy is the study of the parts of the body • Physiology is the study of how the body works